BP has begun pumping cement into the damanged Gulf of Mexico oil well to execute its “static kill” procedure.

The move comes after it was announced that three-quarters of the oil spilled had been cleaned up or broken up or broken down by natural forces.

Oil leaked into the the Gulf from April 20 when the rig exploded and killed 11 workers. The flow was finally stopped on July 15.

Relief wells are still being constructed.

The cementing comes through the top as well as the “bottom kill” that will be carried out shortly.

The relief well is about 100ft from intersecting with the injured well. It will then be killed with cement and mud from the bottom.

A government report said that only a quarter of the oil from the well remains and that is “degrading quickly”.

The majority has been captured, burned off and evaporated, the report says. More clean-up is coming, officials say.

President Obama said on Wednesday that he was pleased with the operation in the Gulf and that it was “finally close to coming to an end”.

"Our recovery efforts, though, will continue. We have to reverse the damage that's been done," he said.

The report on the oil spill was made by 25 of "the best government and independent scientists", according to the National Oceanic and Atmosphere Administration (NOAA).

A quarter or so of the oil released by the well evaporated or dissolved in the Gulf the same way sugar dissolves in water, according to federal officials.

One-sixth naturally dispersed when leaking, and another sixth was burned, skimmed, or dispersed using chemicals.

At a news conference, NOAA official Dr Jane Lubchenco said degraded oil was not a threat any more because "when it is biodegraded it ends up being water and carbon dioxide so if it has been biodegraded, if it is gone, then it is not a threat".

However, almost 53 million gallons of oil remain in Gulf waters, which is about five times the amount of the 11 million gallon Exxon Valdez spill in 1989.

About 4.9 million barrels of oil leaked into the waters of the Gulf during the 87 days, with about 800,000 barrels being captured.